This invention relates to the field of semiconductor devices. More particularly, the present invention relates to an improved package for a semiconductor device and an improved method for packaging semiconductor devices.
Prior art methods for packaging semiconductor devices typically require that a semiconductor device be electrically connected to a printed circuit board. A wire bonding or tape automated bonding process is typically used to connect bonding pads located on the semiconductor device to the bonding pads on the printed circuit board. The printed circuit board and the semiconductor device are then encapsulated to form a packaged semiconductor device.
Recently, packaging techniques which use tape instead of a printed circuit board have been developed for packaging semiconductor devices. The use of tape instead of a printed circuit board gives higher interconnection capability. A typical prior art tape includes a polyimide layer over which a conductive layer is formed. The conductive layer is patterned so as to form bonding pads, an array of contact pads, and interconnects which connect each bonding pad to a contact pad. In one recent design, an opening in the polyimide tape is disposed below each contact pad.
In a typical prior art semiconductor device packaging process that uses tape, a semiconductor device (commonly referred to as a die) is placed over the tape such that the semiconductor device overlies the conductive layer of the tape. Each of the bonding pads is electrically connected to a corresponding bonding pad on the semiconductor device. The wire bonding or tape automated bonding process couples one of the bonding pads on the semiconductor device to one of the bonding pads on the tape.
After the bonding pads are coupled, the resulting assembly is then encapsulated. This encapsulation process typically involves coating or encapsulation of organic material over the semiconductor device. A transfer of molding or glob top coating process is typically used. Next, balls are formed over each of the openings in the polyimide tape such that each of the balls is in electrical contact with one of the contact pads. Since each contact pad is electrically coupled to one of the bonding pads on the semiconductor device, each of the balls are electrically coupled to the semiconductor device.
Each of the balls performs the same function as one of the pins used in a prior art process that uses a printed circuit board. That is, each ball provides connectivity to other devices in the same manner as would a pin. Thus, the balls form a pattern of electrical contacts (hereinafter referred to as a contact pattern) that is required for a particular package. Thus, the contact pattern is the equivalent of a given configuration of pins in a prior art device that uses pins with balls functioning as contacts in place of pins.
This process is repeated for each different semiconductor device to be packaged. That is, a tape having an array of contact pads and bonding pads that meets the specific requirements for each different packaging specification is used to package a particular semiconductor device. For example, a particular semiconductor device may require a contact pattern that has 144 contacts. A tape having 144 bonding pads and 144 contact pads would then be used. The tape would be connected to the semiconductor device and packaged as discussed above, resulting in 144 balls extending from the bottom of the semiconductor package.
In the event that a semiconductor packaging specification called for a contact pattern having 196 contacts, a tape having 196 bonding pads and 196 contact pads would be used to form a packaged semiconductor. The resulting packed semiconductor device would have 196 balls extending from the bottom of the semiconductor package. Some of the more common contact patterns have 128 contacts, 132 contacts, 144 contacts, 180, 196, 208, 256, and 280 contacts.
One of the most significant costs in packaging semiconductor devices using the above-discussed packaging process is the cost of the tape itself. Since different products require different contact patterns, a different configuration of tape must be manufactured for each different product. This is quite expensive since the manufacture and/or purchase of small quantities of tape is quite expensive. Only by purchasing large lots of a particular configuration of tape are the exceedingly high costs of tape reduced. In addition, since many different configurations of tape must be kept in stock, inventory maintenance is quite expensive.
What is needed is a way to more efficiently package semiconductor devices having different packaging requirements. In addition, a method for packaging semiconductor devices which is cost effective, efficient, and which allows for current mass-production packaging methods to be used is required. More particularly, a way to more efficiently package semiconductor devices which will reduce the cost associated with tape is required. The present invention meets the above needs.
The present invention includes a package for a semiconductor device and a method for packaging a semiconductor device which allows for packaging semiconductor devices into packages having different contact pattern requirements using common configurations of tape.
A flexible package for a semiconductor device and a method for packaging a semiconductor device is disclosed. The package includes a tape and an encapsulated organic material. The tape includes a layer of polyimide film over which a conductive layer is deposited. The conductive layer is patterned so as to form an array of contact pads, bonding pads, and interconnects. The interconnects electrically couple each bonding pad to one of the contact pads. Openings are formed in the tape which correspond to each contact pad such that a portion of the bottom surface of each of the contact pads is exposed through a corresponding opening. The number of contact pads and bonding pads on the tape is optimized such that multiple contact patterns may be produced using a common tape configuration.
In operation, a semiconductor device is packaged by placing the semiconductor device onto the tape. The semiconductor device is then electrically coupled to the tape. In one embodiment of the present invention, a tape automated bonding or wire bonding process is used to connect bonding pads of the semiconductor device to bonding pads on the tape using leads. The semiconductor device is then sealed on the top and sides by disposing a plastic top thereover and sealing the plastic top to the tape.
Next, balls are selectively deposited over the bottom surface of the contact pads to make a desired contact pattern. In one embodiment, the contact pads which are not to have balls deposited thereover are sealed using a sealant. Then, solder is applied to the bottom of the tape such that balls are formed over the contact pads which were not sealed. Alternatively, a solder bumping process is used for forming balls (solder bumps) over designated contact pads.
The present invention allows for the mass production of tape since a single configuration of tape may be used to form multiple contact patterns. That is, a tape having a given number of contact pads and bonding pads may be used to make a packaged semiconductor device having a number of contacts which is the same as the number of contact pads and may also be used to make a packaged semiconductor device having a lesser number of contacts and/or a different placement of contacts.
The packaging method of the present invention allows for more efficient packaging of semiconductor devices having different packaging requirements. In addition, the method for packaging semiconductor devices of the present invention is cost effective since there is no need to manufacture different tapes for each contact pattern. Moreover, since there is no need for a special configuration of tape for each contact pattern, inventory requirements and inventory holding costs are reduced.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.